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Ch 12 Volcanos

Ch 12 Volcanos. Igneous Processes. Extrusive Igneous Formations. Volcanoes Openings in the Earth that erupt gases, ash, & lava. Lava flows destroy everything in their path. Pyroclastic flows (ash & debris) rush down the sides of the volcano.

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Ch 12 Volcanos

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  1. Ch 12 Volcanos

  2. Igneous Processes

  3. Extrusive Igneous Formations Volcanoes • Openings in the Earth that erupt gases, ash, & lava. • Lava flows destroy everything in their path. • Pyroclastic flows (ash & debris) rush down the sides of the volcano. • Acid rain is produced when sulfurous gases mix with water vapor in the atmosphere.

  4. Parts of a Volcano • Magma collects in a magma chamber inside the Earth’s crust. • The opening where magma is forced up and flows onto the Earth’s surface is called a vent. • The steep-walled depression around a volcano’s vent is called the crater.

  5. Tephra Vent Magma Chamber

  6. Formation of Volcanoes • Form at Divergent & Convergent plate boundaries. • Hot Spots : • An unusually hot area between the mantle & core that forces melted rock upward to form volcanoes in the middle of tectonic plates. • Plate moves as the hot spot is stationary.

  7. Hawaiian Islands Ring of Fire

  8. 3. Volcanic Eruptions • The explosiveness of a volcano depends on: • Amount of water vapor & other gases trapped in the magma. • Amount of silica present in the magma. - Basaltic lava is low in silica & produces quiet, non-explosive eruptions:

  9. Pāhoehoe(meaning "smooth, unbroken lava” =smooth, billowy, undulating, or ropy surface)

  10. A’a (meaning "stony rough lava” = rough or rubbly surface composed of broken lava blocks) Pāhoehoe lava flowing over a’a Pāhoehoe lava flowing over a’a

  11. - Granitic & andesitic magma are high to intermediate in silica & produce violent eruptions. pyroclastic flow

  12. Types of Volcanoes Shield • Broad volcanoes with gently sloping sides. • Quiet eruptions of basaltic lava forming flat layers.

  13. Cinder Cone • Steep-sided volcanoes made of loosely packed tephra. • Tephra- bits of rock or solidified lava (pyroclastic material) like ash, cinders, bombs, & blocks.

  14. Composite • Volcanoes with alternating layers of tephra & lava flows. • Long dormancy periods • Violent eruptions • Also known as a stratovolcano

  15. Mount St. Helens after May 1980 eruption. Mount St. Helens

  16. Intrusive Igneous Formations Batholiths • Largest intrusive formations • Forms where magma has been forced up into chambers within the crust & cool slowly.

  17. Dikes • Magma that is forced into vertical cracks that cuts across rock layers and hardens.

  18. Sills • Magma that has been forced into cracks that are parallel to rock layers and then hardens.

  19. Volcanic Necks • The solid igneous rock core of an extinct volcano. • Weathering & erosion wear away the cone exposing the neck.

  20. Calderas • Large depression caused by the collapse of a crater during an eruption.

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